PURPOSE: To improve the operability by inhibiting the shock on the connection of the wheeling clutch, when the combine completes the turning and starts running straight in the case where the wheeling clutch and the wheeling brake are controlled by the hydraulic operations to turn the body.

CONSTITUTION: In the pressure control of the hydraulic circuit 41 for the wheeling clutch 8 and wheeling brake 9 by the proportional pressure regulators 43, 46, the hydraulic system is controlled so that the pressure of the regulator valves 43, 46 are lowered down to nearly 0, then the connection pressure of the wheeling clutch 8 is increased, when the operation is switched from the wheeling brake 9 to the wheeling clutch 8 after turning.